Black smoke

[Emilio]

I have a 3300scr with twin 5.7 mer engines and brovo 2 outdrives i have large black smoke at start up in both engines and a gas spill in the water i was told it was un burnt fuel has anyone come across this or give any advise as to what the cause may be and both carbs have been rebuilt thanks

[mmwjr]

Black smoke is unburdened fuel. Are the engines hard to start? Sounds like the carbs are dripping fuel after shut down.

[Emilio]

No thats what i dont understand they start really good and idle good and runs great but there is this black smoke and the slick when they are running not even a bit of hesitation. I just bought the boat a while back and previous own advised that the carbs had been rebuilt im at a loss
Thanks for your reply. Im open to trying anything.

[Phillbo]

Does the smoke clear quickly? Or do they smoke until up to temp?

[mmwjr]

From the description of smoking when first starting I would think blue smoke being oil from leaking valve seal and worn guides. Have you pulled the spark plugs to see how they look?

[Emilio]

No they keep smoking but dose get a little netter

[Emilio]

Its not blue smoke deffinatley black

[Emilio]

No they keep smoking but not as bad but always the slick

[mmwjr]

Have you verified the choke plates are opening all the way? If the carbs were rebuilt their not adjusted properly.

[Emilio]

Yes they are thanks i appreciate all the analysiskeep them coming need to find the problem

[mmwjr]

What carbs; 2 bbl vs 4 bbl, Mercruiser vs Quaderjet vs Weber, ...

[Emilio]

Two barrel

[jparsons121]

I would suspect the carb rebuild was sketchy. Wrong float level adjustment/stuck float will cause the symptoms you describe.
Same with a saturated poly float or a brass one that has a pinhole.

At idle, with flame arrest or off, do you see any fuel bubbling out the breather tube?